The invention relates in general to the construction of filters and particularly to a new and useful air purifier for use with respirators and similar devices.
The invention particularly relates to a process for producing a catalyst for oxidizing carbon monoxide with a carrier of aluminum oxide.
A catalyst of this type is used as air purification means in air filters and is known from the ASME publication of the American Society of Mechanical Engineers, Issue 77-ENAS-28. It will be referred to hereinafter after as Pt-catalyst.
Platinum metals on carrier materials catalyze the conversion of CO, with atmospheric oxygen in this case. This property is utilized on granulated carriers containing platinum metals as filter material for CO-filters. Whereas Hopkalit, which is also known as air purifier for CO-filters, loses its effectiveness under the influence of moisture in the air, the filter material with a Pt-catalyst is largely resistant to humidity. But a certain decline of activity is observed at higher humidity and temporarily also at high CO-concentrations, and a larger volume of filter material must be provided to compensate for these situations. Beside the increased expenditure and need for space, this involves also an additional load on the carrier for the use in respirator filters, for example.
German examined Patent Disclosure No. 22 14 056 discloses a catalyst and a process for producing it that is useful in the reduction of nitrogen compounds. The process involves the addition of palladium and vanadium in a specified percentage by weight to an aluminum oxide carrier. In the process at least 20% of the aluminum oxide that constitutes the carrier material is transformed into spinel.
It has been found that catalyst of this type is not a good catalyst for oxidizing pollutants in air to be breathed, particularly carbon monoxide. The high percentage of spinel in the aluminum oxide tends to prevent it. However, even a reduction of the proportion of spinel does not produce success, because in the presence of moisture and a potentially high proportion of carbon monoxide in the air to be breathed, with the piror art catalyst the oxidation of carbon monoxide is not catalyzed sufficiently, even when the spinel percentage is reduced virtually to nil.